Torque control elements are provided for controlling and/or monitoring steering devices of a motor vehicle. In this context, a steering device is understood to be a steering handle such as a steering wheel, on one hand, but also a steered vehicle wheel or a steered vehicle axle. Torque control elements are used as components of electrical or electronic controlled systems for connecting a steering handle and at least one steered vehicle wheel in a motor vehicle. Such electrical or electronic controlled systems are known as steer-by-wire systems, and replace conventional steering systems in which steered vehicle wheels are mechanically coupled to the steering handle.
German Patent Application No. DE 198 334 60 A1 describes a steering system for acting upon or controlling vehicle wheels. In that case, a mechanical passage is always provided from the steering wheel to the wheels to be coupled. The steering system has two subsystems having one process computer each for calculating control tasks, one servomotor each, one reduction gear each and one power output stage each. The two essentially identical subsystems have the task of complementing one another, especially if a fault occurs, so that the steering system remains functional, even in the case of a fault.
Because of the diverse cabling of individual components of the one subsystem to individual components of the other subsystem, the one subsystem is not independent of the other subsystem. As a result, inoperability of one subsystem, even if only partial, may have an effect on the other system, which can lead to impairment or failure of the entire steering system.
German Patent Application No. DE 198 348 70 A1 describes a steer-by-wire system that is subdivided into two diversely redundant systems, having two servomotors, two control units and two diversely redundant process computers. Each of the two process computers receives information about the driving condition or even the setpoint steering angle to be set, via a data channel from a shared higher-ranking vehicle computer. It is further provided that a process computer of the one system is able to switch off the other system in case of a fault. Reciprocal influencing of the two systems is provided in this related art, as well. A fault within the one system can have an effect on the other system, and thus can impair the functioning of the entire steering system.